Synthesis and characterization of (C5H9C9H6)(2)Yb(THF)(2)(II) (1) and [(C5H9C5H4)(2)Yb(THF)](2)O-2 (2), and ring-opening polymerization of lactones with 1

Reaction of YbI2 with two equivalents of cyclopentylindenyl lithium (C5H9C9H6Li) affords ytterbium(II) substituted indenyl complex (C5H9C9H6)(2)Yb(THF)(2) (1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI2 and cyclopentylcyclopentadienyl sodium (C5H9C5H4Na) gives complex [(C5H9C5H4)(2)Yb(THF)](2)O-2 (2) in the presence of a trace amount of O-2, the molecular structure of which comprises two (C5H9C5H4)(2)Yb(THF) bridged by an asymmetric O-2 unit. The O-2 unit and ytterbium atoms define a plane that contains a C-i symmetry center.

Confined crystallization behavior of PCL in organic-inorganic hybrid system

poly(epsilon-caprolactone) (PCL) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by sol-gel approach and the crystalline behavior of PCL in the silica networks has been investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The degree of PCL crystallinity in the PCL/SiO2 hybrid networks reduces with the increase of SiO2 content. PCL is in an amorphous state when the concentration of PCL is lower than 40wt% in the hybrid materials. The melting points of PCL in the networks are lower than that of pure PCL,but they almost have a same value. WAXD results show that when the PCL weight percentage is higher than 40wt% in the hybrid samples,part of PCL can crysatllize and the PCL crystallites are almost in a same size. That means the crystalline movement of PCL molecular chains is strictly confined by the porous gel. The crystalline PCL in the hybrid samples is relatively free from the composition of the materials, because the crystallization temperature and melting point of PCL of the samples are almost equal,and the crystalline PCL of different samples has the same crystalline structure and the same crystallite sizes L-110 and L-200, that means the crystalline part of PCL in the hybrid samples is unperturbed and the porous silica gel gives enough space for PCL to crystallize into the same crystalline structure and the same size crystallites.

Hydrogel of biodegradable cellulose derivatives. I. Radiation-induced crosslinking of CMC

Radiation crosslinking of carboxymethylcellulose (CMC) with a degree of substitution (DS) from 0.7 to 2.2 was the subject of the current investigation. CMC was irradiated in solid-state and aqueous solutions at various irradiation doses. The DS and the concentration of the aqueous solution had a remarkable affect on the crosslinking of CMC. Irradiation of CMC, even with a high DS, 2.2 in solid state, and a low DS, 0.7 in 10% aqueous solution, resulted in degradation. However, it was found that irradiation of CMC with a relatively high DS, 1.32, led to crosslinking in a 5% aqueous solution, and 20% CMC gave the highest gel fraction. CMC with a DS of 2.2 induced higher crosslinking than that with a DS of 1.32 at lower doses with the same concentration. Hence, it was apparent that a high DS and a high concentration in an aqueous solution were favorable for high crosslinking of CMC. It is assumed that; high radiation crosslinking of CMC was induced by the increased mobility of its molecules in water and by the formation of CMC radicals from the abstraction of H atoms from macromolecules in the intermediate products of water radiolysis. A preliminary biodegradation study confirmed that crosslinked CMC hydrogel can be digested by a cellulase enzyme. (C) 2000 John Wiley & Sons, Inc.

Phase behavior of polymer blends

The present report deals with some results on phase behavior, miscibility and phase separation for several polymer blends casting from solutions. These blends are grouped as the amorphous polymer blends, blends containing a crystalline polymer or two crystalline polymers. The blends of PMMA/PVAc were miscible and underwent phase separation at elevated temperature, exhibited LCST behavior. The benzoylated PPO has both UCST and LCST nature. For the systems composed of crystalline polymer poly(ethylene oxide) and amorphous polyurethane, of two crystalline polymers poly(epsilon-caprolactone) and poly[3,3,-bis-(chloromethyl) oxetane], appear a single T-g, indicating these blends are miscible. The interaction parameter B's were determined to be -14 J cm(-3), -15 J cm(-3) respectively. Phase separation of phenolphthalein poly(ether ether sulfone)/PEO blends were discussed in terms of thermal properties, such as their melting and crystallization behavior.

Crystallization behavior of PCL in hybrid confined environment

Poly(epsilon -caprolactone) (PCL) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by the sol-gel method. The crystallization behavior of PCL in silica networks has been investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The degree of PCL crystallinity in PCL/SiO2 hybrid networks reduces with increase of SiO2. PCL is in an amorphous state when the concentration of PCL is lower than 40wt% in the hybrid system. The melting point of PCL in the networks is lower than, but close to that of pure PCL. WAXD and SEM results show that the crystalline behavior of PCL in PCL/SiO2 hybrid system is strictly confined. (C) 2001 Elsevier Science Ltd. All rights reserved.

A novel method of studying polymer biodegradation

A novel combination of laser light scattering (LLS) and the micronization of a water-insoluble polymer into narrowly distributed nanoparticles stable in water has provided not only an accurate, reliable and microscopic method to study polymer biodegradation, but also a novel and fast way to evaluate the biodegradability of a given polymer. Using poly(epsilon-caprolactone) (PCL) as a typical example, we have shown that its biodegradation time can be shortened by a factor of more than 10(3) times in comparison with the time required to biodegrade a thin film (10 x 10 x 0.1 mm(3)). Moreover, the biodegradation kinetics can be in-situ monitored in terms of the decrease of the time-average scattering intensity and the particle number. A comparison of static and dynamic LLS results revealed that the enzyme, Lipase Pseudomonas, ''eats'' the PCL nanoparticles in an one-by-one manner and the enzymatic biodegradation of PCL follows a zero-order kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.

A novel rare earth coordination catalyst for polymerization of biodegradable aliphatic lactones and lactides

A novel rare earth coordination system composed of lanthanide trifluoroacetates Ln(CF3COO)(3) (Ln = Y, Yb, Nd, Tm, Ho, La, Pr) and triisobutylaluminium Al(i-Bu)(3) was used as catalyst for the polymerization of epsilon-caprolactone (CL), D,L-lactide (DLLA) and their copolymerization. The influence of temperature, time and catalyst concentration on polymerization yields and molecular weights of the polyesters have been studied. It was shown that the ring-opening polymerization of cyclic esters catalysed by Ln(CF3COO)(3)/Al(i-Bu)(3) has some living character and the molecular weight of the polyester could be controlled by adjusting the molar ratio of monomer to catalyst. The DLLA/CL copolymer was synthesized by sequential addition of monomers and the structure of the copolyester was characterized by GPC, NMR and DSC. (C) 1998 SCI.

Application of digital image analysis to the study of banded spherulite during growing and melting process

A digital image analysis(DIA) technique can be applied directly to the image obtained by polarizing microscope. The time-resolved DIA apparatus including image collecting, showing and data analysis has been home-made. As an example, it has been used to study the banded spherulite in the blends of poly(epsilon-caprolactone) (PCL) and poly(styrene-ran-acrylonitrile) (SAN).

The miscibility of homopolymer random copolymer blends .3. Blends of SAA with polymethacrylates and polyesters

The miscibility of blends of poly(styrene-co-allyl alcohol) (SAA) with poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(n-butyl methacrylate) (PnBMA), poly-epsilon-caprolactone (PCL) or polycarbonate (PC) has been studied by means of NMR, FT-IR and DSC techniques. It was found that SAA and PMMA, PEMA or PCL form miscible blends and SAA is only partially miscible with PC or PnBMA. Both phenyl groups and hydroxyl groups in SAA are involved in the intermolecular interactions between SAA and PMMA, PEMA or PCL. Also the hydroxyl-carbonyl hydrogen bonds existing in all the miscible blends studied are formed partially at the expense of the disruption of self-association of hydroxyl groups in pure SAA. (C) 1997 Elsevier Science Ltd. All rights reserved.

Poly(epsilon-capralactone)/poly(ethylene oxide) diblock copolymer .2. Nonisothermal crystallization and melting behavior

The nonisothermal crystallization behavior and melting process of the poly(epsilon-caprolactone) (PCL)/poly(ethylene oxide) (PEG) diblock copolymer in which the weight fraction of the PCL block is 0.80 has been studied by using differential scanning calorimetry (DSC). Only the PCL block is crystallizable, the PEO block with 0.20 weight fraction cannot crystallize. The kinetics of the PCL/PEO diblock copolymer under nonisothermal crystallization conditions has been analyzed by Ozawa's equation. The experimental data shows no agreement with Ozawa's theoretical predictions in the whole crystallization process, especially in the later stage. A parameter, kinetic crystallinity, is used to characterize the crystallizability of the PCL/PEO diblock copolymer. The amorphous and microphase separating PEO block has a great influence on the crystallization of the PCL block. It bonds chemically with the PCL block, reduces crystallization entropy, and provides nucleating sites for the PCL block crystallization. The existence of the PEO block leads to the occurrence of the two melting peaks of the PCL/PEO diblock copolymer during melting process after nonisothermal crystallization. The comparison of nonisothermal crystallization of the PCL/PEO diblock copolymer, PCL/PEO blend, and PCL and PEO homopolymers has been made. It showed a lower crystallinity of the PCL/PEO diblock copolymer than that of others and a faster crystallization rate of the PCL/PEO diblock copolymer than that of the PCL homopolymer, but a slower crystallization rate than that of the PCL/PEO blend. (C) 1997 John Wiley & Sons, Inc.

Synthesis of lanthanide-alkylaluminium bimetallic complexes and studies on their catalytic activities for polymerization of some polar monomers

Three new lanthanide (Ln)-alkylaluminium (Al) bimetallic complexes with the formula [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AIR(2) . 2THF](2) (Ln = Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF,CO,), (Ln=Nd, Y) with HAI (i-Bu)(2) and of Eu(CF3CO2)(3) with AlEt(3), respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(mu-CF3CO2)(2)Nd (mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Nd-Al) and [(mu-CF3CO2)(2)Y(mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Y-Al) are isomorphous and crystallize in space group with a=12.441(3) Angstrom [12.347(5) Angstrom for Y-Al], b=12.832(3) Angstrom [12.832(4) Angstrom], c=11.334(3) Angstrom [11.292(8) Angstrom], alpha=104.93 (2)degrees [104.45(4)degrees], beta=98.47(2)degrees [98.81(4)degrees], gamma=64.60(2)degrees [64.30(3)degrees], R=0.519 [0.113], R(w)=0.0532 [0.110], Z=1 and [(mu-CF3CO2)(2)Eu(CF3CHO2)AlEt(2) . 2THF](2)(Eu-Al) in space group P2(1)/n with a=11.913(6) Angstrom, b=14.051(9) Angstrom, c=17.920(9) Angstrom, alpha=101.88(11)degrees, beta=gamma=90 degrees, R=0.0509, R(w)=0.0471 and Z=2. The six CF3CO2- (including CF3CHO2-) of each complex, among which pairs are equivalent, coordinated to Ln and Al in three patterns: (A) the two oxygen atoms in one of the three CF3CO2- type coordinated to two different Ln; (B) the two oxygen atoms in the second of CF3CO2- type coordinated to Ln and Al, respectively; (C) one of the two oxygen atoms in the third CF3CO2- type bidentately coordinated to two Ln and another oxygen coordinated to Al and one of the two Ln, respectively. Unlike types A and B, in type C the carboxyl carbon with a hydrogen atom bonded to it was found to appear as an sp(3)-hybridized configuration rather than an sp(2)-one. 1D and 2D NMR results further confirmed the existence of such a disproportionated CF3CHO2- ligand. Methyl methacrylate (MMA) and epichlorohydrin (ECH) could be polymerized by Y-Al or Eu-Al as a single-component catalyst and highly syndiotactic poly(MMA) was obtained. THF could also be polymerized by Y-Al in the presence of a small amount of ECH.

Study of semicrystalline-amorphous diblock copolymers .1. Microphase separation, glass transition and crystallization of tetrahydrofuran methyl methacrylate diblock copolymers

The microphase separation, glass transition and crystallization of two series of tetrahydrofuran-methyl methacrylate diblock copolymers (PTHF-b-PMMA), one with a given PTHF block of M(n) = 5100 and the other with a given PTHF block of (M) over bar(n) = 7000, were studied in this present work. In the case of solution-cast materials, the microphase separation of the copolymer takes place first, with crystallization then gradually starting in the formed PTHF microphase. The T-g of the PMMA microphase shows a strong dependence on the molecular weight of the PMMA block, while the T-g of the PTHF microphase shows a strong dependence on the copolymer composition. The non-isothermal crystallization temperature (T-c) of the diblock copolymer decreases rapidly and continuously with the increase in the amorphous PMMA weight fraction; the lowest T-c of the copolymer is ca. 35 K lower than the T-c of the PTHF homopolymer. There also exists a T-c dependence on the molecular weight of the PTHF block. In addition, when the major component of the copolymer is PMMA, a strong dependence of the crystallizability of the copolymer on the molecular weight of the PTHF block is observed; the higher the molecular weight, then the stronger its crystallizability. The melting temperature of the block copolymer is dependent on the copolymer composition and the molecular weight of its crystallizable block. Copyright (C) 1996 Elsevier Science Ltd.

COMPATIBILITY AND CRYSTALLIZATION OF TETRAHYDROFURAN-METHYL METHACRYLATE DIBLOCK COPOLYMER/POLYTETRAHYDROFURAN BLENDS

The compatibility and crystallization of tetrahydrofuran-methyl methacrylate diblock copolymer (PTHF-b-PMMA)/tetrahydrofuran homopolymer (PTHF) blends were studied. Our results showed that the crystallization and morphology of compatible PTHF-b-PMMA/PTHF

MISCIBILITY OF POLY(HYDROXYETHER OF PHENOLPHTHALEIN) WITH POLY(ETHER SULFONE)

Blends of poly(hydroxyether of phenolphthalein) (PHP) with poly(ether sulphone) (PES) were prepared by casting from a common solvent; they were found to be miscible and show a single, composition-dependent glass transition temperature. All the PHP/PES blends exhibited lower critical solution temperature behaviour, i.e. phase separation occurred at elevated temperatures. A F.T.-i.r. study revealed that a hydrogen-bonding interaction occurs between these polymers but it is weaker than in pure PHP. The observed miscibility is hence proposed to be the result of specific interactions between the polymers.

Chondrogenesis and mineralization during in vitro culture of human mesenchymal stem cells on three-dimensional woven scaffolds.

Human mesenchymal stem cells (hMSCs) and three-dimensional (3D) woven poly(ɛ-caprolactone) (PCL) scaffolds are promising tools for skeletal tissue engineering. We hypothesized that in vitro culture duration and medium additives can individually and interactively influence the structure, composition, mechanical, and molecular properties of engineered tissues based on hMSCs and 3D poly(ɛ-caprolactone). Bone marrow hMSCs were suspended in collagen gel, seeded on scaffolds, and cultured for 1, 21, or 45 days under chondrogenic and/or osteogenic conditions. Structure, composition, biomechanics, and gene expression were analyzed. In chondrogenic medium, cartilaginous tissue formed by day 21, and hypertrophic mineralization was observed in the newly formed extracellular matrix at the interface with underlying scaffold by day 45. Glycosaminoglycan, hydroxyproline, and calcium contents, and alkaline phosphatase activity depended on culture duration and medium additives, with significant interactive effects (all p < 0.0001). The 45-day constructs exhibited mechanical properties on the order of magnitude of native articular cartilage (aggregate, Young's, and shear moduli of 0.15, 0.12, and 0.033 MPa, respectively). Gene expression was characteristic of chondrogenesis and endochondral bone formation, with sequential regulation of Sox-9, collagen type II, aggrecan, core binding factor alpha 1 (Cbfα1)/Runx2, bone sialoprotein, bone morphogenetic protein-2, and osteocalcin. In contrast, osteogenic medium produced limited osteogenesis. Long-term culture of hMSC on 3D scaffolds resulted in chondrogenesis and regional mineralization at the interface between soft, newly formed engineered cartilage, and stiffer underlying scaffold. These findings merit consideration when developing grafts for osteochondral defect repair.